Protein kinases are a large group of intracellular and transmembrane signaling proteins in eukaryotic cells. These enzymes are responsible for transfer of the terminal (gamma) phosphate from ATP to specific amino acid residues of target proteins. Phosphorylation of specific tyrosine, serine or threonine amino acid residues in target proteins can modulate their activity leading to profound changes in cellular signaling and metabolism. Protein kinases can be found in the cell membrane, cytosol and organelles such as the nucleus and are responsible for mediating multiple cellular functions including metabolism, cellular growth and division, cellular signaling, modulation of immune responses, and apoptosis. The receptor tyrosine kinases are a large family of cell surface receptors with protein tyrosine kinase activity that respond to extracellular cues and activate intracellular signaling cascades (Plowman et al. (1994) DN&P, 7(6):334-339).
Aberrant activation or excessive expression of various protein kinases are implicated in the mechanism of multiple diseases and disorders characterized by benign and malignant proliferation, excess angiogenesis, as well as diseases resulting from inappropriate activation of the immune system. Thus, inhibitors of select kinases or kinase families are expected to be useful in the treatment of cancer, autoimmune diseases, and inflammatory conditions including, but not limited to: solid tumors, hematological malignancies, arthritis, graft versus host disease, lupus erythematosus, psoriasis, colitis, illeitis, multiple sclerosis, uveitis, coronary artery vasculopathy, systemic sclerosis, atherosclerosis, asthma, transplant rejection, allergy, dermatomyositis, pemphigus and the like.
Examples of kinases that can be targeted to modulate disease include receptor tyrosine kinases such as members of the platelet-derived growth factor receptor (PDGFR), vascular endothelial growth factor receptor (VEGFR) families and intracellular proteins such as members of the Syk, SRC, and Tec families of kinases.
Tec kinases are non-receptor tyrosine kinases predominantly, but not exclusively, expressed in cells of hematopoietic origin (Bradshaw J M. Cell Signal. 2010, 22:1175-84). The Tec family includes Tec, Bruton's tyrosine kinase (Btk), inducible T-cell kinase (Itk), resting lymphocyte kinase (Rlk/Txk), and bone marrow-expressed kinase (Bmx/Etk). Btk is a Tec family kinase which is important in B-cell receptor signaling. Btk is activated by Src-family kinases and phosphorylates PLC gamma leading to effects on B-cell function and survival. Additionally, Btk is important in signal transduction in response to immune complex recognition by macrophage, mast cells and neutrophils. Btk inhibition is also important in survival of lymphoma cells (Herman, SEM. Blood 2011, 117:6287-6289) suggesting that inhibition of Btk may be useful in the treatment of lymphomas.
cSRC is the prototypical member of the SRC family of tyrosine kinases which includes Lyn, Fyn, Lck, Hck, Fgr, Blk, Syk, Yrk, and Yes. cSRC is critically involved in signaling pathways involved in cancer and is often over-expressed in human malignancies (Kim L C, Song L, Haura E B. Nat Rev Clin Oncol. 2009 6(10):587-9). The role of cSRC in cell adhesion, migration and bone remodeling strongly implicate this kinase in the development and progression of bone metastases. cSRC is also involved in signaling downstream of growth factor receptor tyrosine kinases and regulates cell cycle progression suggesting that cSRC inhibition would impact cancer cell proliferation. Additionally, inhibition of SRC family members may be useful in treatments designed to modulate immune function. SRC family members, including Lck, regulate T-cell receptor signal transduction which leads to gene regulation events resulting in cytokine release, survival and proliferation. Thus, inhibitors of Lck have been keenly sought as immunosuppressive agents with potential application in graft rejection and T-cell mediated autoimmune disease (Martin et al. Expert Opin Ther Pat. 2010, 20:1573-93).
Inhibition of kinases using small molecule inhibitors has successfully led to several approved therapeutic agents used in the treatment of human conditions. Herein, we disclose a novel family of kinase inhibitors. Further, we demonstrate that modifications in compound substitution can influence kinase selectivity and therefore the biological function of that agent.
PCT Publication Nos. WO02/080926 and WO02/76986 disclose pyrazolopyrimidines as therapeutic agents. Btk is included in a long list of biologically un-related kinases. No evidence of kinase inhibition or cellular activity was disclosed in WO02/080926 and exemplification centers on amide and sulfonamide derivatives with a limited subset of unsubstituted 4-phenoxyphenyl derivatives.
U.S. Pat. No. 7,514,444 discloses inhibitors of Btk. Compound 13 (PCI-32765) of this patent has been reported to show ATP competitive binding to a wide range of kinases including Btk, Lck, Lyn, cSRC, Jak, EGFR, KDR and others (Honigberg, L. A, et al, The Bruton tyrosine kinase inhibitor PCI-32765 blocks B-cell activation and is efficacious in models of autoimmune disease and B-cell malignancy, PNAS vol. 107 no. 29, 13075-13080). Specifically for Btk, the acrylamide functionality of compound 13 is reported to covalently bind the thiol moiety of Cys481, which is situated adjacent to the ATP binding pocket of Btk, thus inducing “sustained” inhibition of Btk. However, compound 13 also inhibits various kinases which also feature a Cys adjacent to the ATP binding pocket, such as Bmx, Tec, Txk, Itk, EGFR, ErbB2, ErbB4, Jak3 and Blk. Covalent binding to any of these kinases may diminish the selective nature of this approach.
GDC-0834 belongs to a structurally unrelated family of compounds which were recently reported to demonstrate significant Btk selectivity (Liu L., et al, Antiarthritis effect of a novel Bruton's tyrosine kinase (BTK) inhibitor in rat collagen-induced arthritis and mechanism-based pharmacokinetic/pharmacodynamic modeling: relationships between inhibition of BTK phosphorylation and efficacy. J Pharmacol Exp Ther. 2011 July; 338(1):154-63). GDC-0834 was active in several animal models of autoimmune disease. However, this compound failed in Phase 1 clinical trials as a result of human specific metabolism (Liu L, et al, Significant species difference in amide hydrolysis of GDC-0834, a novel potent and selective Bruton's tyrosine kinase inhibitor, Drug Metab Dispos. 2011 October; 39(10): 1840-9).
Inhibition of EGFR has been related to the induction of severe rash with multiple clinical compounds (Tan A R, et al, Markers in the epidermal growth factor receptor pathway and skin toxicity during erlotinib treatment. Ann Oncol. 2008 January; 19(1):185-90). Similarly, inhibition of KDR (VEGFR2) has been clinically related to hypertension (Howard R. Mellor, et al., Cardiotoxicity Associated with Targeting Kinase Pathways in Cancer, Toxicological Sciences 120(1), 14-32 (2011). Therefore, the development of Btk inhibitors which demonstrated greater kinase selectivity could potentially be useful in various B-cell related indications which require acute and/or chronic dosing regimens, such as cancer, inflammatory and autoimmune diseases.
The present invention relates to a family of potent and selective, non-covalent Btk inhibitors which demonstrate cellular activity, oral exposure and activity in animal models of inflammation and autoimmune disease. Kinase selectivity and cellular potency are related to specific substitution patterns on the compounds. Synthetic methods are disclosed which provide compounds on multi-gram scale.